MALDI imaging mass spectrometry as a novel tool for detecting histone modifications in clinical tissue samples

SUMMARY

Histone post-translational modifications (PTMs), histone variants and enzymes responsible for the incorporation or the removal of the PTMs are being increasingly associated with human disease. Combinations of histone PTMs and the specific incorporation of variants contribute to the establishment of cellular identity and hence are potential markers that could be exploited in disease diagnostics and prognostics and therapy response prediction. Due to the scarcity of suitable antibodies and the pre-requirement of tissue homogenization for more advanced analytical techniques, comprehensive information regarding the spatial distribution of these factors at the tissue level has been lacking. MALDI imaging mass spectrometry provides an ideal platform to measure histone PTMs and variants from tissues while maintaining the information about their spatial distribution. Discussed in this review are the relevance of histones in the context of human disease and the contribution of MALDI imaging mass spectrometry in measuring histones in situ.

KEYWORDS:

• Histone modifications
• MALDI-IMS
• disease markers
• nuclear density
• clinical tissue samples

Financial & competing interests disclosure

Work in the Imhof lab was supported by a grant from the European Union FP7 Network of Excellence EpiGeneSys (Project 257082), the DFG Excellence Clusters, CIPSM and Munich cluster for Systems Neurology, SyNergy. Work in the Walch lab was supported by the Ministry of Education and Research of the Federal Republic of Germany (BMBF) (Grant No. 01ZX1310B and SysStomach 01ZX1310B) and the Deutsche Forschungsgemeinschaft (Grant Nos. HO 1254/3-1, SFB824 TP Z02, and WA 1656/3-1) to A Walch. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Key Issues

• Histone family of proteins is an integral part of gene expression and regulation machinery in eukaryotes.

• Histones are extensively posttranslationally modified proteins. Alteration in the steady-state of these modifications and/or the dynamics of establishment/removal of these marks is associated with a wide range of diseased conditions.

• Progress in high-throughput detection of histones has been limited owing to the lack of specific and selective antibodies for histone PTMs and variants. Moreover, antibodies cannot provide the level of multiplicity required for analyzing combinatorial effects of different histone modifications and variants.

• MALDI-IMS provides a potential platform, where multiple histone PTMs and isoforms could be detected directly from tissue surfaces, thereby maintaining intact spatial and diagnostic information.

• Recently, we have developed a workflow that enables detection and identification of histone PTMs and variants based on an intrinsic property of eukaryotic cells, i.e. the presence of nucleus. The method is general in application and can be considered for any type of healthy or diseased tissue.

• Our MALDI-IMS-based method is currently the only one that has the desired specificity, multiplicity, and generality that is required for histone analysis in clinical samples. This method could potentially develop into a powerful tool for high-throughput epigenetic screening of diseased states.

• Lastly, integration of upcoming IMS techniques and methods and a combined multi-analyte measurements on the same IMS platform could provide a comprehensive idea about the epigenetic landscape in a particular diseased state.